250 Marine Macro- and Microalgae: An Overview
however, requires a strict balance to be sought between feedstock farming and economic development
(Kalam and Masjuki 2002). Reduced emissions make biodiesel suitable for use in major cities where air
pollution is a problematic. In addition, its lower emissions make biodiesel suitable for use in confined
areas such as mines where ventilation is a concern. Pure biodiesel has low aquatic toxicity and more
than 90% biodiesel can be biodegraded within 21 days (Mudge and Pereira 1999; Speidel et al. 2000).
This property substantially reduces the impact of accidental spills and makes this liquid fuel an ideal
candidate for use in environmentally sensitive areas, such as inland water ways. As a useful by-product,
oxygen is produced by the photoautotrophic feedstock from which biofuels are made. Oxygen makes up
almost 10% (w/w) of biodiesel, making it a naturally “oxygenated” fuel. As an oxygenated hydrocarbon,
biodiesel itself burns cleanly but it also improves the efficiency of combustion in blends with petroleum
fuel (Murayama 1994). Biodiesel hydrocarbon chains are generally 16–20 carbons in chain length, and
they are all oxygenated at one end, making the product an excellent fuel, which is safe for transport due
to its high flash point (130ºC), which is significantly higher than that of petrodiesel (64ºC) (Knothe 2006).
At present two common standards of biodiesel fuel exists: American ASTM D6751 and European EN
14214 (Demirbas 2009).
Bioethanol properties
Bioethanol is one of the most commonly used biofuel worldwide, particularly in Brazil and the USA.
It is a clear colourless, food-grade liquid that burns to produce carbon dioxide and water; it is less
harmful to the atmosphere than fossil fuel, readily biodegradable, and its use produces fewer air-borne
pollutants than that of petroleum fuel if spilt. Bioethanol is a high-octane fuel and it can also be used to
replace octane enhancers such as methyl-tert-butyl ether (MTBE), methyl-cyclopentadienyl-manganese
tricarbonyl (MMT), and aromatic hydrocarbons in petrol (Champagne 2007). Blending bioethanol with
petrodiesel, can also oxygenate the fuel mixture, burning it more completely, and thereby reducing
polluting emissions. Ethanol fuel blends are widely sold in the United States. The most common blend is
E10 (10:90; ethanol and petrol). Automobile engines do not require any modifications to run on E10 and
vehicle warranties are also unaffected. Only flexible fuel vehicles can run on up to E85 (15:85; petrol and
ethanol) with conventional fuel without the need of engine modifications. Bioethanol has the advantage
of being a renewable resource, contributing to the mitigation of greenhouse gas emissions by preventing
further burning of fossil fuels. In addition, using bioethanol in older engines can help reduce the amount
of carbon monoxide produced by the vehicle, thus improving air quality. Another advantage of bioethanol
is the ease with which it can be integrated into the existing road transport fuel system. Bioethanol can also
be used in rocket engines or internal combustion engines in its pure form (Pfromm et al. 2010).
Biogas properties
Biogas is a mixture of methane (55–75%) and CO 2 (25–45%) (Harun et al. 2010b; Jasvinder and Gu 2010)
including minor amounts of hydrogen sulphide (H 2 S), nitrogen, siloxanes, and moisture. Biogas may be
not suitable to be used as fuel gas for transportation/or machinery, due to the high amount of carbon
dioxide, which can be upgraded into a mixture of biomethane and carbon dioxide with a more favourable
ratio: 97% biomethane and 2% CO 2 . Biomethane is environmentally friendly and CO 2 neutral, due to the
life cycle of it. There are both emissions and mitigations that balance and produce a net reduction in GHG
(i.e., CO 2 ) when compared to natural gas (i.e., fossil fuel). Biomethane is being used as vehicular fuel gas
and to generate electricity as well as for cooking and heating purposes (Holm et al. 2009).
Feedstocks for biofuel manufacture
There is increasing interest in alternative fossil fuels from various sources including food, municipal
and agricultural wastes, vegetable oils, animal fat, as well as microalgal biomass as feedstocks for the
production of biofuel worldwide. Biofuels such as biodiesel, bioethanol, and biogas differ from fossil
fuels in their chemical nature, as they are derived from first generation feedstocks such as food-based
however, requires a strict balance to be sought between feedstock farming and economic development
(Kalam and Masjuki 2002). Reduced emissions make biodiesel suitable for use in major cities where air
pollution is a problematic. In addition, its lower emissions make biodiesel suitable for use in confined
areas such as mines where ventilation is a concern. Pure biodiesel has low aquatic toxicity and more
than 90% biodiesel can be biodegraded within 21 days (Mudge and Pereira 1999; Speidel et al. 2000).
This property substantially reduces the impact of accidental spills and makes this liquid fuel an ideal
candidate for use in environmentally sensitive areas, such as inland water ways. As a useful by-product,
oxygen is produced by the photoautotrophic feedstock from which biofuels are made. Oxygen makes up
almost 10% (w/w) of biodiesel, making it a naturally “oxygenated” fuel. As an oxygenated hydrocarbon,
biodiesel itself burns cleanly but it also improves the efficiency of combustion in blends with petroleum
fuel (Murayama 1994). Biodiesel hydrocarbon chains are generally 16–20 carbons in chain length, and
they are all oxygenated at one end, making the product an excellent fuel, which is safe for transport due
to its high flash point (130ºC), which is significantly higher than that of petrodiesel (64ºC) (Knothe 2006).
At present two common standards of biodiesel fuel exists: American ASTM D6751 and European EN
14214 (Demirbas 2009).
Bioethanol properties
Bioethanol is one of the most commonly used biofuel worldwide, particularly in Brazil and the USA.
It is a clear colourless, food-grade liquid that burns to produce carbon dioxide and water; it is less
harmful to the atmosphere than fossil fuel, readily biodegradable, and its use produces fewer air-borne
pollutants than that of petroleum fuel if spilt. Bioethanol is a high-octane fuel and it can also be used to
replace octane enhancers such as methyl-tert-butyl ether (MTBE), methyl-cyclopentadienyl-manganese
tricarbonyl (MMT), and aromatic hydrocarbons in petrol (Champagne 2007). Blending bioethanol with
petrodiesel, can also oxygenate the fuel mixture, burning it more completely, and thereby reducing
polluting emissions. Ethanol fuel blends are widely sold in the United States. The most common blend is
E10 (10:90; ethanol and petrol). Automobile engines do not require any modifications to run on E10 and
vehicle warranties are also unaffected. Only flexible fuel vehicles can run on up to E85 (15:85; petrol and
ethanol) with conventional fuel without the need of engine modifications. Bioethanol has the advantage
of being a renewable resource, contributing to the mitigation of greenhouse gas emissions by preventing
further burning of fossil fuels. In addition, using bioethanol in older engines can help reduce the amount
of carbon monoxide produced by the vehicle, thus improving air quality. Another advantage of bioethanol
is the ease with which it can be integrated into the existing road transport fuel system. Bioethanol can also
be used in rocket engines or internal combustion engines in its pure form (Pfromm et al. 2010).
Biogas properties
Biogas is a mixture of methane (55–75%) and CO 2 (25–45%) (Harun et al. 2010b; Jasvinder and Gu 2010)
including minor amounts of hydrogen sulphide (H 2 S), nitrogen, siloxanes, and moisture. Biogas may be
not suitable to be used as fuel gas for transportation/or machinery, due to the high amount of carbon
dioxide, which can be upgraded into a mixture of biomethane and carbon dioxide with a more favourable
ratio: 97% biomethane and 2% CO 2 . Biomethane is environmentally friendly and CO 2 neutral, due to the
life cycle of it. There are both emissions and mitigations that balance and produce a net reduction in GHG
(i.e., CO 2 ) when compared to natural gas (i.e., fossil fuel). Biomethane is being used as vehicular fuel gas
and to generate electricity as well as for cooking and heating purposes (Holm et al. 2009).
Feedstocks for biofuel manufacture
There is increasing interest in alternative fossil fuels from various sources including food, municipal
and agricultural wastes, vegetable oils, animal fat, as well as microalgal biomass as feedstocks for the
production of biofuel worldwide. Biofuels such as biodiesel, bioethanol, and biogas differ from fossil
fuels in their chemical nature, as they are derived from first generation feedstocks such as food-based